Method of fabricating a cathode ray tube



Jan. 25, 1966 K. A. BARNES METHOD OF FABRICATING A CATHODE RAY TUBE Filed Sept. 25, 1962 INVENTOR BY mgr/1 4 570 5 W #TflZ W0 M H.\ fl ,w 6 A M1 2 4k y 1 W- 1 Q r\ 5 g 0 4 I /Z u /3 F 2 V a y 00 //o8 4 2 n 0 5 United States Patent 3,230,600 METHOD OF FABRLCATING A CATHQDE RAY TUBE Keith A. Barnes, Marion, Ind, assignor to Radio Corporation of America, a corporation of Delaware Filed Sept. 25, 1962, Ser. No. 226,035 3 Claims. (Cl. 29;25.13)

This invention relates to cathode ray tubes and particularly to a method of fabricating electron guns therefor.

One type of electron gun, such as those of cathode ray tubes used in monochrome television receivers, usually comprises a plurality of electrodes including a cathodecontrol-grid assembly and a screen grid mount-ed along a plurality of insulator rods. Each of the electrodes is supported on the rods by a plurality of wire-like or straplike elements which are embedded in the rods and usually welded to the electrode. Alternatively, the support elements may be provided as integral parts of the electrodes extending therefrom which are embedded in the insulator rods.

The cathode-control-grid assembly of such electron guns comprises a cup-shaped control grid which is provided with an aperture centrally in the end wall thereof and a cathode assembly which is mounted within the grid cup. The control grid is supported by support elements embedded in the insulator support rods. The cathode assembly comprises a tubular cathode sleeve supported coaxially in the aperture of a ceramic washer which has one or more short tubular retaining rings secured to its periphery. The cathode sleeve has an end wall which is coated with electron emissive material. The retaining rings are such as to permit the cathode assembly to be telescopically slid into the grid cup with the retaining rings in snug contact with the internal cylindrical surface of the grid cup. The retaining rings are then fixed to this surface, e.g., by welding, so as to maintain the emissive end wall of the cathode in a desired spaced relationship with the apertured wall of the grid cup.

Because of the snug fit of the cathode assembly within the grid cup, considerable force must be applied to both the cathode assembly and the control grid cup in order to telescope them together. In performing this telescopic assembly according to prior art practice, the control grid cup has been backed-up by means designed to bear against the electrode support elements which are attached to the grid cup and embedded in the insulator rods. However, when this practice has been followed, difficulty has been encountered in obtaining the desired cathode-togrid spacing and in maintaining the control grid-to-screen grid spacing which was established during the mounting of these electrodes onto the insulator support rods.

This invention is based in part on an appreciation of the fact that if the grid cup is held by its support elements, the force of sliding the cathode assembly into the grid cup causes the support members to be sprung or bent slightly during the telescopic assembly operation. When the operation is completed and the sliding force removed, the support elements experience a spring-back to the extent that they have not exceeded their elastic limit. Such bending results in the cathode-control grid pacing being set on the basis of a control grid-screen grid spacing which changes due to spring-back after the spacing operation is completed. The effects of this is that for the actual control grid-screen grid spacing of the finished gun the cathode-control grid spacing is too great. In many cases, in addition to such a spring-back, a permanent distortion produced in the electrode support elements causes a decrease in the pre-established, desired spacing between the control grid and the screen grid.

It is therefore an object of this invention to provide a means of and method of frictionally sliding a cathode assembly into a control grid cup whereby a desired cathodeto-grid spacing may be accurately obtained and whereby the spacing of the control grid from the screen grid is not adversely affected.

In accordance with this invention, in an electron gun of the type described, the control grid cup is provided with an annular transverse wall portion axially spaced from the apertured end wall thereof. Such transverse wall portion may, for example, comprise an outward radial flange at the open end of the cup. The grid cup and other electrodes of the gun are mounted in close spaced relationship with each other on a plurality of in.- sulator support rods. The cathode assembly is then frictionally telescoped into the control grid cup while the cup is backed-up by an element of a jigging fixture bearing against the annular transverse wall portion thereof. Excessive force need not therefore be applied to the support elements attached to the grid cup during insertion of the cathode therein.

In the drawings:

FIG. 1 is a side elevation view partly in section and with parts broken away of a cathode ray tube embodying the invention; A

FIG. 2 is an enlarged detail in section of the cathodegrid assembly of the tube of FIG. 1;

FIG. 3 is a partial section View illustrating apparatus useful for practicing the method of this invention; and

FIG. 4 is a section taken along lines 44 of FIG. 3.

The invention may be embodied in a cathode ray tube 10 such as that shown in FIG. 1. The tube 10 includes an envelope comprising a neck section 12, a faceplate 14, and an interconnecting funnel section 16. An electron gun 1'8 in the neck 12 is adapted to project an electron beam onto a target in the form of a luminescent screen 19 on the faceplate 14. The screen 19 may be of any suitable type such as one comprising a layer 20 of phosphor material on the faceplate with a superimposed film 21 of evaporated aluminum thereupon.

The electron gun 18 comprises a plurality of coaxial, tubular, centrally-apertured electrodes including a control electrode cup 22, a screen electrode cup 24, and a focussing system including a first anode 26, a focussing ring 28, and a second anode 30. These electrodes are mounted in coaxial spaced relationship along a pair of insulator rods 32 by U-shaped mounting studs 34 which are fixed to the electrodes and embedded in the insulator rods. A cathode assembly 35 which includes a tubular cathode 36 is mounted in a centrally apertured insulator disk, e.g., a ceramic washer 38, which is coaxially mounted within the control electrode cup 22. The cathode 36 is closed at one end with an end wall at which is coated with suitable materials to provide an electron emissive surface. A heater filament 41 is provided within the tubular cathode 36..

A conductive coating 42 on the internal surface of the funnel 16 is connected to the luminescent screen 19 and to the second anode 30 through a plurality of spring snubbers 44 attached to the second anode. A high voltage contact terminal indicated schematically by the arrow 46 is provided for applying a suitable voltage to the coating 42, the second anode 30, the phosphor screen 19, and the first anode 26 which may be connected (not shown) to the anode 30 internally of the tube.

The neck 12 is closed at its distal end with a stem structure (not shown) over which a base 48 is fixed. A plurality of lead-in conductors 50 for applying suitable voltages to electrodes of the electron gun 18 are sealed through the stem and extend through the base 48.

Referring to FIG. 2, the control grid cup 22 comprises a cylindrical wall 51 which is closed at one end with a planar transverse wall 52 and which is provided With an annular transverse wall portion in the form of an outwardly extending radial flange 53 at the other end. The end wall 52 has an electron beam aperture 54 centrally thereof. The cathode assembly 35 comprises the cathode 36, the ceramic washer 38, and two flanged tubular retaining rims 56 and 58. The tubular cathode 36 is secured within the aperture of the ceramic washer 38 by a pair of circumferentially crimped beads 60 which are part of the cylindrical wall 36 and which are flattened against the opposite flat faces of the washer. The ceramic washer 38 is held captive axially between the flanged outer rim 56 and the flanged inner rim 58. The inner rim 8 fits snugly radially within the outer rim 56 and is fixed thereto such as by welding. The end wall 40 of the cathode is provided with a coating 61 of suitable electron emissive material. The cathode assembly 35 is positioned as a unit within the grid cup 22 to obtain a desired spacing of the emissive coated end wall 40 of the cathode from the apertured end wall 52 of the grid cup. Electrical welds are then made to fix the cylindrical walls 62 and 64 of the rims 56 and 58 to the inside surface of the cylindrical wall 51 of the cathode cup 22.

'In fabricating the electron gun 18, the electrodes 22, 24, 26, 28, and 30 are first mounted in their desired space-d relationship on the insulator rods 32 by the U-shaped, wire-like support studs 34, as shown in FIG. 1. The cathode assembly 35, comprising the cathode 36, the ceramic washer 38, and the two retaining rims 56 and 58, is pre-assembled as a unit as described with reference to FIG. 2. The cathode assembly 35 is then telescopically mounted within the grid cup 22 of the electrode assembly, as illustrated in FIG. 3.

Referring to FIGS. 3 and 4, the assembly of electrodes 22, 24, 26, 28 and 30 (only part of which is shown) is placed in a fixture 70. The fixture 70 may comprise upper and lower members (not completely shown) having elements for contacting and positioning the electrodes. Such upper and lower members include shaped back-up elements 72 adapted to receive the control grid cup 22 in seated relationship therewith. The upper and lower members may be hinged relative to each other so that they are closable on the electrodes. The elements 72 abut the flange 53 on its front surface 74 (see also FIG. 2), which faces the closed end of the grid cup 22, and thereby back-up the grid cup 22 against an axial force being applied thereto in the direction from right to left, as viewed in FIG. 3.

A guide member 76 is pressed against the grid cup flange 53 by a coil compression spring 78 to hold the grid cup 22 against theback-up elements 72. The cathode assembly 35, previously pre-assembled, is telescopically mounted (not shown) over a mandrel 80 within the guide member 76. The gun support fixture 70 is axially driven relative to the mandrel Si by suitable manual or electric drive means (not shown) to telescopically slide the cathode assembly into the grid cup 22 to a desired position.

In positioning the cathode assembly 35 within the grid cup 22, a capacitance measuring technique is preferably used. In such a technique, a capacitance measurement between the cathode and another of the electrodes, for example, the screen grid 24, is taken and compared with a standard capacitance which is indicative of the desired cathode-to-control grid spacing. As shown in FIG. 3, a contact plunger 84 is insulatingly mounted within the fixture 70 and is adapted to make electrical contact with the screen grid 24. Contact with the cathode is made vvia the mandrel 80 and the frame of the fixture 70. Arrows 86, 87 and 88 represent terminal means to which a suitable capacitance bridge device (not shown) may be coupled in order to obtain the desired capacitance measurement.

As will be noted from the set-up of FIGS. 3 and 4, the control grid cup 22 is supported and backed-up exclusive of any substantial force being applied to the support studs 34 which support the control grid on the insulator rods 32. Instead, the entire back-up force is applied by the back-up elements 72 against the flange 53 of the grid cup. As a result, the harmful effects of grid spring-back and changed spacing between the control grid 22 and screen grid 24, as encountered in prior art practice, are avoided.

What is claimed is:

1. The method of fabricating a cathode ray tube having an electron gun comprising a plurality of electrodes including a centrally apertured control grid cup mounted along an insulator support rod and a cathode assembly including a cathode sleeve snugly mounted concentrically within said grid cup, said method comprising the steps of:

(a) forming said grid cup with an annular transverse wall portion axially spaced from the closed end thereof,

(b) mounting said electrodes including said grid cup on said insulator rod,

(0) then frictionally sliding said cathode assembly telescopically into said grid cup to a desired position while backing up said grid cup against its said annular transverse wall and measuring the capacitance between said cathode sleeve and another of said electrodes to determine said desired position, and

(d) then fixing said cathode assembly to said grid cup in said desired position.

2. The method of fabricating a cathode ray tube having an electron gun comprising a plurality of electrodes including a centrally apertured control grid cup mounted along a plurality of insulator support rods, and a cathode assembly comprising a ceramic washer having a cathode sleeve supported within the aperture of said washer and a retaining rim fixed to the periphery of said washer, said cathode assembly being mounted concentrically within said grid cup, said method comprising the steps of:

(a) forming said .grid cup with an outwardly extending radial flange at the open end thereof,

(b) mounting said electrodes including said flanged grid cup in close spaced relationship along said insulator rods,

(c) then frictionally sliding said cathode assembly telescopically into said flanged grid cup to a desired position While backing up said grid cup against the radial flange thereof and measuring the capacitance between said cathode sleeve and another of said electrodes to determine said desired position, and

(d) then welding said retaining rim of said cathode assembly to said grid cup in said desired position.

3. The method of fabricating a cathode ray tube having an electron gun comprising a plurality of electrodes including a centrally apertured cup-shaped control grid coaxially mounted along a plurality of insulator support rods by wine-like support elements attached to said electrodes and anchored in said insulator rods, and a cathode assembly comprising a tubular cathode sleeve supported within the aperture of a ceramic Washer which has a retaining rim fixed to the periphery thereof, said cathode assembly being mounted concentrically within said cupshaped control grid with the retaining rim thereof frictionally engaging the side wall of said cup-shaped control lgrid, said method comprising the steps of:

(a) forming said cup-shaped control grid with an outwardly extending radial flange at the open end thereof,

(b) mounting said electrodes including said flanged cup-shaped control grid in close spaced relationship along said insulator rods,

(0) contacting said radial flange of said cup-shaped control grid on the side thereof facing the closing end of said cup-shaped control grid with means to back up said cup-shaped control grid against an axial force being applied thereto in the direction from its open end toward its closed end,

5 6 ((1) then frictionally sliding said cathode assembly References Cited by the Examiner telescopically into said cup-shaped control grid to UNITED STATES PATENTS a desired position, whereby such an axial force is applied to said cup-shaped control grid, while meas- 2582454 1/1952 Pomeuring the capacitance between said cathode sleeve 5 4 and another of said electrodes to determine said de- QTHER REFERENCES sired position, and R.C.A. Technical Note No. 306, by Raymond C. Paull, (e) then welding said retaining rim of said cathode as- November 1959- sembly to the side wall of said cup-shaped control grid with said cathode assembly in said desired posi- 10 GRANVILLE S ER, 111., Primary Examiner.

tion. FRANK E. BAILEY, Examiner. 

1. THE METHOD OF FABRICATING A CATHODE RAY TUBE HAVING AN ELECTRON GUN COMPRISING A PLURALITY OF ELECTRODES INCLUDING A CENTRALLY APERTURED CONTROL GRID CUP MOUNTED ALONG AN INSULATOR SUPPORT ROD AND A CATHODE ASSEMBLY INCLUDING A CATHODE SLEEVE SNUGLY MOUNTED CONCENTRICALLY WITHIN SAID GRIP CUP, SAID METHOD COMPRISING THE STEPS OF: (A) FORMING SAID GRID CUP WITH AN ANNULAR TRANSVERSE WALL PORTION AXIALLY SPACED FROM THE CLOSED END THEREOF, (B) MOUNTING SAID ELECTRODES INCLUDING SAID GRID CUP ON SAID INSULATOR ROD, (C) THEN FRICTIONALLY SLIDING SAID CATHODE ASSEMBLY TELE- 